Drying apparatus and method



1943. D. D. PEEBLES 2,310,650

' DRYING APPARATUS AND METHOD Filed Aug. 2, 1940 INVENTOR fla /a eeb/esWham ATTORNEY Patented Feb. 9, 1943 DRYING APPARATUS AND METHOD David D.Peebles, Berkeley, Oalifl, assignor to Golden State Company, Ltd., SanFrancisco, Calif a corporation of Delaware Application August 2, 1940,Serial No. 349,420

6 Claims. (01. 159-17) This invention relates generally to apparatus andprocesses for the manufacture of various powdered products from liquidmaterials. The invention is particularly applicable to the manufactureof various powdered milk products from lacteal materials such as skimmilk.

It is an object of the invention to provide an apparatus and process ofthe above character which will be capable of relatively high operatingeconomy.

A further object of the invention is to generally improve upon apparatusand processes such 4 as make use of a spray drier in conjunction with agas washer. The present invention is characterized by the use of a heatexchanger in the liquid circulating path of the washer, and thisexchanger also serves as a condenser for evaporating apparatus whichrare-concentrates the liquid material being treated.

Additional objects and features of the invention will appear from thefollowing description in which the preferred embodiment of the inventionhas been set forth in detail in conjunction with the accompanyingdrawing.

The apparatus illustrated diagrammatically in the attached drawingconsists of a suitable spray drier III by means of which liquid materialcanbe converted to powder, As representative of suitable spray dryingequipment, I have shown apparatus such as disclosed in my co-pendingapplication Serial No. 349,419, filed Aug. 2, 1940;

Briefly, the spray drier consists of a desiccating chamber l I, intowhich hot drying gas is continuously introduced by conduit I2 and heaterl3. Conduit l2 connects with an annular conduit l4 surrounding the upperportion of the desiccating chamber. Circumferentially spaced louvers l6communicate between annular conduit l4 and the upper portion of thedesiccating chamber, whereby the inflowing gas is directed in atangential direction to cause a cyclonic movement of gas in thedesiccating zone. A cluster of nozzles l1 serves to introduce the liquidmaterial in finely atomized form into the deslccating chamber. Since theindividual nozzles are spaced vertically and circumferentially, and arefaced at angles of about 45 with respect to radii from the central axis01 the chamber in the direction of swirling gas currents, the materialis in effect atomized into a substantially cylindrically shaped primarydrying zone. The majority of the dry powdered material is removed fromthe lower end of chamber it, together with some gas from within thechamber. e

To effect a final drying the material passes through a secondary chamberl8 which connects with the discharge conduit l9. Conduit l9 dischargesinto separator 20, the exhaust from which is returned to secondarychamber I 8 by conduit 2|. Another conduit 22 connects with chamber l8for introducing additional drying gas. Conduits 2| and 22 connecttangentially to cause cyclonic movement in chamber it in the samedirection as in chamber it.

The desiccating chamber is also provided with an exhaust conduit 23which connects axially of the chamber through the top wall, and throughwhich a large proportion of the gas is withdrawn together with someentrained powdered material. A baiiie 23a is interposed between theinlet end of conduit 23 and the nozzles l1. Conduit 23 is shownconnected to a washer 24, whereby the exhaust gases are scrubbed withliquid for the removal of entrained powder. This washer can consist of achamber 25 having a gas exhaust conduit 26, and having its interiorequipped with spray head 21.

one or more liquid spray heads 21. The lower end of chamber 25 connectswith a liquid drain pipe The liquid supplied to the washer 24 is liquidmaterial being supplied to the, process. Tank 29 is shown for storage ofthis material, and pump 30 serves to deliver the liquid material throughpipes 3i and 28 to a heat exchangeunit 33. Line 34 represents a part ofthe liquid discharging from heat exchanger 33 being supplied to the Inorder to maintain a constant level of liquid in the lower part of thewasher, pipe 3| is shown provided with a valve 38, controlled by theinner float 31. Pipe 3| thus discharges into the washer chamber 25 at arate suflicient to-maintain the level of liquid within the chambersubstantially constant. Pump 38 in pipe line 28 delivers this liquidunder a proper pressure head to the heat exchanger 33 and to the sprayhead 21.

Pipe 40 connects the discharge side of heat eitchanger 33 with theliquid inlet of the evaporat oi the type disclosed and claimed inPeebies and Manning Patent 2,090,984, which utilizes relativeiy highflow velocities through evaporating tubes. Pump 42 serves to introduceliquid from pipe 40 into the first efiect A. and liquid together withevolvedv vapor from this eifect passes through the separating trap 43.Separated liqtrap (I. is removed by way 01' line 44 for introductioninto the second effect B. Line 46 represents introduction of steam intothe jacket of the first effect A, while the jacket of the second effectis connected by conduit '41 with the trap 43. Lines 48 and 49 representremoval of condensate and non-condensables from the lower portions ofboth heating jackets.

Liquid withdrawn from the first effect through line 44 is delivered tothe second unit B for further concentration. Vapor removed from theseparator 52 of Unit B is delivered by line 53 to the heat exchange unit33. Concentrate from separator 52 is removed by pump 55 and delivered byline 54 to the storage tank 56. From tank 56 the material is supplied tothe nozzles of the spray drier by pump 51 and line 58. s

The heat exchanger 33 can be of the closed tube type in which the tubesthrough which the liquid circulates are heated by being contacted withvapor received through conduit 53. Pipe 59, communicating with the lowerpart of the heating jacket, connects with suitable means for removal ofcondensate and non-condensables.

Operation of the apparatus described above, and the carrying out of thepresent process, can be outlined as follows: It will be presumed that alacteal material such as raw skim milk is being treated for the purposeof producing a dry powdered product. This liquid material is deliveredfrom tank 29 through pipes 3i and 28 to theheat exchanger 33. As theskim milk leaves the heat exchanger 33, it is at an elevatedtemperature, and this temperature is delivered in part to the spray head21 of the washer 24. Within this washer the liquid is intermingled withgas being received from the spray drier l0, and thus solid particles aretaken up by the liquid from the gas, while the washed gas dischargesthrough the conduit 26. The liquid collecting in the lower part of thewasher is re-circulated through the heater 33. This collected liquid isat a substantially lower temperature than the temperature' of liquidsupplied to pipe 34 and spray head 21, due toevaporation of moisturewithin chamber 25, while the liquid material is in contact with gas fromthe spray drier. Evolved vapor is absorbed by the gas from conduit 23and passesout through conduit 26.

That part of the liquid material which is diverted from the heatexchanger 33 by way of line 40 enters the first efiect A of theevaporating apparatus. Concentrated liquid material being withdrawn bypump 55 from the second effect B is delivered by pipe 54, tank 56, pump51 and line 58 to the atomizing nozzles of the spray drier I0. Wherehigher concentrations are required than are possible with a single passthrough the two efiects of the evaporating apparatus, a certain amountof the concentrate delivered by pump 55 can be returned to the firststage by way of line 6|.

A partial vacuum is maintained upon the evaporating apparatus by virtueof the fact that the heat exchange unit 33 serves as a condenser forvapor supplied through conduit 53'. Thus, the heat exchanger 33 servestwo important functions, namely it serves to preheat liquid beingcirculated through the washer 24, and it also serves as a condenser tomaintain a partial vacuum upon the evaporating apparatus.

In one instance in which th invention was used for the purpose ofproducing dry skim milk powder, the raw skim milk was delivered by pump38 at a temperature of 130 F., and was discharged from heat exchanger 33at a temperature of 157 F.

With respect to operation of the washer 24, spraying the liquid materialwithin this washer not only serves to remove and recover powderentrained with gas exhausting from the spray drier, but in addition asubstantial amount of vapor is evolved from the hot liquid, which vaporis exhausted through conduit 26. Thus, liquid material being circulatedthrough the washer is subjected to concentration by.evaporation, inaddition to subsequent concentration in the evaporating apparatus 4 I.

Because of the particular way in which the heat exchanger 33 isincorporated in the apparatus and process, the invention affords utmostoperating economy. Also, the apparatus is capable of high capacity for agiven size of spray drier employed.

I claim:

1. In processes for treatment of liquid materials to produce powderedproducts, whereinthe raw liquid material is first circulatedsuccessively through preheating and washing operations and is thenconcentrated in an evaporating operation, after which it is subjected tospray drying, the spray drying operation being characterized by exhaustof gas from a desiccating zone together with some powdered material, theexhaust gases being supplied to the washing operation, the improvementcomprising utilizing vapor evolved in the evaporating operation forsupplying heat to the preheating operation, whereby conditions ofpartial vacuum are maintained for the material being evaporated andwhereby heated vapor evolved in the evaporating operation is utilized toheat liquid material being circulated through the washing operation andbeing supplied to the evaporating operation.

2. In processes for treatment of liquid materials to produce powderedproducts, wherein the liquid material is successively preheated,concentrated by evaporation and then subjected to a. spray dryingoperation, the spray drying operation being characterized by continuousremoval of drying gas from the desiccating zone together with someentrained powder, the improvement comprising the steps of continuouslyre-circulating liquid material into contact with said gas to removeentrained powder from the gas, preheating the liquid material being sore-circulated by transferring heat to the same from vapor evolved fromthe evaporating operation, and continuously diverting a part of theliquid material being recirculated for-supplying the same to theevaporating operation.

3. In processes for treatment of liquid materials to produce powderedproducts, characterized by use of spray drying apparatus, a washerreceiving gas exhausted from said spray drying apparatus, a vacuumevaporator, and a heat transfer unit for preheating raw material beingsupplied to the process, the steps of continuously circulating the rawliquid material through said heat transfer unit and through the washer,diverting a part of the liquid material being so circulated andintroducing the same into the vacuum evaporator to effect concentrationof the same, supplying the concentrate to the spray drier, and conveyingthe vapor evolved from the vacuum evaporator to the heat transfer unit,whereby the heat transfer unit serves to condense such vapor.

4. In apparatus for the treatment of liquid materials to producepowdered products, spray drying apparatus adapted to convert liquidmaterial into powder, said apparatus having an exhaust conduit forremoving gas together with some entrained powdered material, a washerconnected to said conduit, a heat, exchange unit, means for circulatingliquid material through said heat exchange unit and through said washer,vacuum evaporating apparatus, a connection serving to divert part of theliquid material circulating through the heat exchange unit to theevaporating apparatus, a connection serving to supply concentrate fromthe evaporating apparatus to the spray drier, and means for forming avapor connection from the evaporating apparatus.

to said heat transfer unit, whereby the heat transfer unit serves as acondenser for the evaporating apparatus.

5. In processes for treatment of liquid materials to produce powderedproducts, wherein the liquid material is first concentrated byevaporation and then subjected to a sp y drying peration, the spraydrying operation being characterized by continuous removal of drying gasfrom the desiccating zone together with some entrained powder, theimprovement comprising the step of condensing vapor evolved from theliquid material in the evaporating operation by transfering heat fromsuch vapor to liquid material being supplied to the process, and washinggases withdrawn from said desiccation zone by contact with liquidmaterial passed through said last named step, whereby said liquidmaterial is cooled, and reusing said liquid material after such coolingfor condensing vapor evolved from the liquid material in the evaporatingoperation.

6. In processes for treatment of liquid materials to produce powderedproducts, wherein the liquid material is first concentrated byevaporation and then subjected to aspray drying operation, the spraydrying operation being characterized by continuous removal of drying gasfrom the desiccating zone together with some entrained powder, theimprovement comprising the step of condensing vapor evolved from theliquid material in the evaporating operation, utilizing for thecondensing operation a heat exchange operation in which heat absorbedfrom the vapor is transferred to liquid material being supplied to theprocess, washing gases withdrawn from said desiccating zone by contactwith liquid material immediately after it has passed through said lastDAVID D. PEEBLES.

